<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="jquery.min.js"></script>
    <style>
        .nav {
            width: 200px;
            height: 200px;
            background-color: pink;
        }
    </style>
</head>
<body>
    <div class="nav"></div>
    <ul>
        <li>aaaa</li>
        <li>ssssss</li>
        <li>cccccc</li>
    </ul>
</body>
<script>
    //jquery基础选择器 $("选择器名")
    console.log($(".nav"));
    //设置属性：$("选择器").css("属性"，"值");
    //隐式迭代，不用循环。
    $("li").css("background-color", "blue");
</script>
</html>